In semiconductor processing technology, wafers of a semi-conducting material are frequently processed for diffusion or oxidation in a reactor chamber. For instance, in a low pressure chemical vapor deposition reactor, a large number of wafers can be accommodated for each run. The wafers can be stacked side by side with only a few mm apart in a quartz reaction tube. The wafers are positioned in wafer holders, or sometimes called wafer boats, which can hold up to 200 wafers. When the wafers are held vertically and separated from each other by a narrow space, maximum wafer capacity can be achieved in a reaction chamber. When wafers are positioned in a diffusion or oxidation furnace, the wafers are placed perpendicular to a gas flow in a quartz tube that has a circular cross-section.
When designing a reactor, the geometry of the reactor is restricted by the pressure regime and the energy source of the reactor. The reactor geometry is also an important factor in the throughput of the reactor. Since atmospheric pressure reactors normally operate in the mass-transport-limited regime, the reactors must be designed such that an equal flow of reactants can be delivered uniformly to each wafer. As a result, it is more desirable to stack the wafers horizontally by laying them flat on a horizontal surface instead of stacking vertically at close spacing. An undesirable consequence of the horizontal wafer layout is the higher susceptibility of the wafers to be contaminated by falling particles.
A horizontal reactor consists of a quartz tube, radiantly heated by a multi-zone furnace. The reactor pressure ranges between about 0.2 Torr and about 2.0 Torr while the temperature ranges between about 250.degree. C. and about 950.degree. C. A vertical furnace operates essentially in the same manner as the horizontal furnace, except for the orientation of the wafers. In a vertical furnace, the wafers are loaded in a horizontal position by a wafer tweezer onto a quartz cassette which can be either lowered or raised into the furnace by an elevator device. One other benefit achieved by a vertical furnace over a horizontal furnace is that only a reduced area needs to be occupied in a clean room environment, and the reduced contamination during wafer processing.
One of the key steps involved in processing wafers in a vertical furnace requires the use of a wafer tweezer to load wafers into a wafer boat from cassettes. The wafer tweezer is frequently constructed of a quartz material in order to withstand high temperature and corrosive chemical exposures. A conventional wafer tweezer used to load wafers into a wafer boat is shown in FIG. 1.
Tweezer assembly 10 that has tweezer blades 12 mounted in a chuck base 14 is shown in FIG. 1 for loading wafers 18 into a wafer boat 22. The wafer boat 22 is generally machined of a quartz material with a plurality of wafer receptacles 24. The tweezer assembly 10 shown in FIG. 1 is commonly used in the loading of six-inch wafers. In a typical wafer boat such as that shown in FIG. 1, the pitch between the receptacles is approximately 4.76 mm and the height of each receptacle is approximately 2.5 mm. Since a typical six-inch wafer has a thickness of 0.67 mm, this leaves a space of approximately 0.9 mm between the wafer surface and the surface of the receptacles. During the loading of wafers into a wafer boat from a tweezer assembly, it is critical to have a very tight tolerance of the spacings between the tweezer blades such that the wafers may be loaded into the boat without touching the edges of the receptacles. The tweezer blades 12 are normally constructed of a quartz material and have a thickness of approximately 1.5 mm. The distance allowed between the tweezer blades in an assembled position is approximately 3.26 mm. The mounting of the tweezer blades 12 in chuck base 14 is therefore a very important step in a semiconductor processing technology. If tweezer blades 12 are not properly mounted in chuck base 14, the wafer loading process may cause damages to the wafers when the wafers are accidentally pushed into the walls 26 of the wafer boat 22.
A conventional process for assembling a wafer tweezer assembly 10 is shown in FIGS. 2A and 2B. In FIG. 2A, a perspective view of the various components of the tweezer assembly 10 is shown. In FIG. 2B, an end view of the components of the tweezer assembly 10 is shown. It is seen, in FIG. 2A, that a plurality of chuck plates 28 are assembled to form the chuck base 14. A plurality of Teflon gaskets 32 of approximately 0.1 mm thick are used as a seal between tweezer blades 34 and chuck plates 28. Vacuum ports 36 are provided in the tweezer blades 34, the Teflon gaskets 32 and the chuck plates 28 such that vacuum can be applied through slot openings 38 in the surface of tweezer blades 34 to securely hold wafers 18. At the top of each tweezer, silicon rubber gaskets 42 of approximately 0.5 mm thick are used as vacuum seals to keep each tweezer as a vacuum chamber independently. Vacuum can be applied through vacuum holes 36, slot opening 38 and vacuum holes 44 at the tip section of the tweezer blade 34 to hold the wafers.
FIG. 2B is an end view of an unassembled chuck base 10 consisting of chuck plates 28, Teflon gaskets 32 and tweezer blades 34. Mechanical means, such as four bolts 48 are used to fasten the plurality of chuck plates 28, the Teflon gaskets 32, the silicon rubber gasket 42 and the tweezer blades 34 together. In the assembling process for chuck base 14, the position of the tweezer blades 34 in relation to the chuck plates 28 is determined by the Teflon gaskets 32 and the silicon rubber gaskets 42. There is no reliable method available for calibrating the exact distance between the tweezer blades 34 such that wafers can be precisely positioned on top of the tweezer blades.
In assembling the tweezer assembly 10 shown in FIG. 2A, there is no assembly aid or guide which can be used for determining the position of the tweezer blades 34 and the gaskets 32, 42 in relation to the chuck plates 28. The assembling process for the tweezer assembly is therefore very difficult to execute. Moreover, the horizontal accuracy and the gap tolerance are difficult, or impossible to calibrate during such assembly.
It is therefore an object of the present invention to provide a wafer tweezer assembling device that can be easily utilized to assemble a wafer tweezer assembly.
It is another object of the present invention to provide a tweezer assembling device that can be used as a guide for fixing the positions of the various components in a tweezer assembly.
It is a further object of the present invention to provide a tweezer assembling device that performs not only the assembling function but also the calibration function simultaneously.
It is another further object of the present invention to provide a tweezer assembling device that can be utilized to assemble a wafer tweezer together without the need for further calibration procedures.
It is yet another object of the present invention to provide a tweezer assembling device that can be repeatedly used for assembling tweezer assemblies.
It is still another object of the present invention to provide a tweezer assembling device that utilizes spacers of a predetermined thickness for fixing the positions of the tweezer blades such that no further calibration is required.
It is still another further object of the present invention to provide a method for assembling and calibrating a wafer tweezer assembly simultaneously by utilizing a tweezer assembling device equipped with spacers of a predetermined thickness.
It is yet another further object of the present invention to provide a method for using a calibrated wafer tweezer assembly to load wafers into a process chamber by first utilizing a tweezer assembling device to assemble and calibrate a tweezer assembly.